Wireless communication systems for performing data communication between terminals using high-frequency signals are widely used. In such a wireless communication system, if a frame transmitted from a transmission terminal collides with another frame or if the signal strength of the frame is low, the frame from the source may not reach a destination. Therefore, in the transmission terminal in the wireless communication system, an acknowledgement (Ack) method is generally used in which proper arrival of transmitted data in the destination is confirmed by receiving an Ack frame from the destination.
In such an acknowledgement method, a source performs a retransmission process of retransmitting the same data as transmitted data if the source cannot receive an Ack frame from the destination within a certain time period. If the source cannot receive an Ack frame even after the source has performed such a retransmission process a certain number of times, the source changes a frame modulation scheme to a modulation scheme that is more resistant to interference and further repeatedly performs the retransmission process.
The change to a modulation scheme resistant to interference causes an increase in frame length. Thus, in a network with traffic congestion, a collision rate between frames increases, which may further increase the traffic. For the purpose of suppressing the increase in traffic caused by such a change of the modulation scheme, there has been suggested a method for determining whether or not the cause of not being able to receive an Ack frame is collision. For example, there has been suggested an apparatus for detecting the energy level of a reception signal in a period when the reception of an Ack message is expected (for example, see PTL 1).